1. Field of the Invention
The invention is in the field of traffic coordinators, particularly those coordinators utilized for controlling arterial systems.
2. Description of the Prior Art
Many different types of traffic control systems have been devised in the prior art to meet particular traffic needs. Typically, traffic controllers are located at an intersection and may be either pretimed or traffic actuated devices. Many attempts have been made to coordinate the operation of the various controllers. Simple systems utilize time clocks or simple program units to coordinate a plurality of timers to thereby permit progressive traffic flow patterns. More sophisticated systems utilize a separate master coordinator (traffic computer) unit which may be programmed to control arterial systems or a complete grid network. Examples of such prior art systems are shown, for example, in U.S. Pat. Nos. 3,818,429, 3,660,812, 3,506,808, 3,258,745, 3,307,146 and 3,252,133. Typically, traffic control systems provide means for determining cycle lengths, offset and split information by utilizing either traffic actuated vehicle detectors to monitor traffic flow or stored parameter programs set to correspond to historical data for the intersection or artery under consideration. U.S. Pat. No. 3,258,745, for example, illustrates a traffic control system for an artery utilizing traffic actuating controllers and permitting adaptive control of split data in response to vehicle presence. U.S. Pat. No. 3,506,808, for example, discloses the utilization of both volume and occupancy detectors to determine appropriate cycle length in an analog computing and control system. Digital processing techniques for a traffic control system are shown, for example, in U.S. Pat. No. 3,818,429. Most of these prior art systems, however, lack the flexibility necessary to control a large number of traffic conditions, are complicated to install and control no provisions for coordinated operation during communication breakdown. Additionally, prior art coordinated traffic systems do not permit a means for achieving different cycle lengths simultaneously throughout the coordinated system to follow a platoon of vehicles through the system. As a consequence, cycle length is typically changed throughout the entire system at one time so that the coordinated system cannot truly operate to optimize the traffic flow pattern for the different platoons travelling therein.